Analogues of the cyclic peptide beauvericin will be synthesized to produce agents that will transport with high specificity a single cation through biological membranes. The ion of most interest is calcium, an active component and regulator of muscle contraction, cellular surface activity, mitochondrial activity, and non-steroid hormone activity. This proposal promises to provide basic information relevant to peptide conformation, ionic selectivity, ion transport, lipid membranes and drug design. Methods will involve both, conventional and solid-phase peptide synthesis. Evaluation of the products will be by NMR and UV spectroscopy as well as by X-ray crystallography and by fast pulsed lipid bilayer membrane conductivity measurements. In addition assays of mitochondrial metabolism and heart muscle metabolism will be employed.